1. Field of the Invention
The present invention relates to an air-dynamic bearing apparatus and a polygon scanner motor.
2. Description of the Related Art
In an optical system such as a laser beam printer and a digital copier, there is used a polygon scanner motor as means for scanning laser beam. According to a motor apparatus for driving a polygon mirror used for such use, high accuracy and high speed rotation are requested and accordingly, an air-dynamic bearing is widely used as a rotational bearing for supporting a rotor of the motor fixed with the polygon mirror. In an air-dynamic bearing of this kind, a radial bearing portion and a thrust bearing portion are generally formed and to enable to satisfy the above-described request, it is preferable in view of wear resistance that all of parts are constituted by ceramic parts.
However, it is difficult to fabricate a ceramic part having a complicated shape and accordingly, it is necessary to fabricate a desired air-dynamic bearing by integrating ceramic parts each having a simple shape. Therefore, there poses a problem that a number of parts is increased, further, a ceramic part is expensive and therefore, an air-dynamic bearing in which all of parts are constituted by ceramic parts become extremely expensive.
Hence, there has conventionally been proposed an air-dynamic bearing which is inexpensive and is provided with a long service life by using an inexpensive metal material such as aluminum as a material therefor and coating a resin layer on a dynamic face of a metal member fabricated by aluminum to thereby promote wear resistance. However, when the resin coating is used, there poses other problem that it is necessary to refabricate grooves or outer dimensions after coating and the productivity is poor.
In order to resolve the problems, there is disclosed a bearing of a motor in which a shaft member is formed by aluminum or aluminum alloy, a radial dynamic bearing is formed by coating lubricating resin on an outer peripheral face of the shaft member and a thrust bearing is constituted by using a magnet in Japanese Patent Laid-Open No. 219146/1996.
However, according to the bearing disclosed in Japanese Patent Laid-Open No. 219146/1996, the thrust bearing is constituted by using the magnet and therefore, a number of parts is large, time is taken in assembling, the cost is increased and when disturbance is caused in rotating thereof, up and down movement is produced in the axial direction and a reflecting face of a side face of a polygon mirror moves in an up and down direction. Therefore, there poses a problem that influence of mirror face accuracy is liable to be effected and adverse influence is liable to be effected on scanning by laser beam.
It is an object of the invention to provide an air-dynamic bearing apparatus capable of constituting a radial dynamic bearing and thrust dynamic bearings by a small number of parts by using a metal material which is easy to fabricate and a polygon scanner motor using thereof.
In order to resolve the above-described object, according to an aspect of the invention, there is provided an air-dynamic bearing apparatus for rotatably supporting a rotating member comprising a metal material relatively by a shaft member comprising a metal material, the air-dynamic bearing apparatus comprising a small diameter shaft portion integrally formed with a front end portion of the shaft member for rotatably supporting an attaching hole of the rotating member, and a dynamic pressure generating member fixed to an end portion of the small diameter shaft portion, wherein a radial dynamic bearing is formed between the small diameter shaft portion and an inner peripheral face of the attaching hole, a first thrust dynamic bearing is formed between one end face of the rotating member and a corresponding face of the shaft member, a second thrust dynamic bearing is formed between other end face of the rotating member and a corresponding face of the dynamic pressure generating member and respective dynamic faces of the radial dynamic bearing, the first thrust dynamic bearing and the second thrust dynamic bearing are protected by low friction metal plating layers.
The metal material can be a material easy to fabricate such as aluminum or an aluminum alloy.
The radial dynamic bearing can be constituted by providing a groove for generating dynamic pressure at least at either one side of a dynamic face comprising an outer peripheral face of the small diameter shaft portion and an inner peripheral face of the attaching hole.
The first thrust dynamic bearing can be constituted by providing a groove for generating dynamic pressure at least at either one side of a dynamic face comprising a plane portion of the shaft portion which is brought into contact with a lower end of the small diameter shaft portion and one end face of the rotating member.
The second thrust dynamic bearing can be constituted by providing a groove for generating dynamic pressure at least at either one side of a dynamic face comprising other end face of the rotating member and a corresponding face of a holding member.
According to another aspect of the present invention, there is provided a polygon scanner motor constituted by fixing a polygon mirror formed with a reflecting face for scanning light at a side face thereof to a rotating member comprising a metal material, wherein a rotating member is rotatably supported relatively by a shaft member comprising a metal material on a side of a stator by an air-dynamic bearing apparatus, the air-dynamic bearing apparatus comprising a small diameter shaft portion integrally formed with a front end portion of the shaft member for rotatably supporting an attaching hole of the rotating member, and a dynamic pressure generating member fixed to an end portion of the small diameter shaft portion, a radial dynamic bearing is formed between the small diameter shaft portion and an inner peripheral face of the attaching hole, a first thrust dynamic bearing is formed between one end face of the rotating member and a corresponding face of the shaft member, a second thrust dynamic bearing is formed between other end face of the rotating member and a corresponding face of the dynamic pressure generating member and respective dynamic faces of the radial dynamic bearing, the first thrust dynamic bearing and the second thrust dynamic bearing are protected by low friction metal plating layers.